Posted
by
kdawson
on Friday May 21, 2010 @09:14AM
from the duck-and-cover dept.

An anonymous reader notes the discovery of a 35-million-year-old impact crater in the Timor Sea, northwest of Australia, which helped to usher in a period of significant global cooling. "The new findings, announced today and published in the Australian Journal of Earth Sciences, suggest that the impact could have contributed towards the formation of the Antarctic ice sheet... The minimum size of the dome, which 'represents elastic rebound doming of the Earth crust triggered by the impact' is 50 km across, but the full size of the crater could be significantly larger, [lead researcher Andrew Glikson] told Australian Geographic. 'It would be possibly 100 km.' From the probable diameter of the crater, Andrew estimates that the asteroid which struck the Timor Sea was between 5 and 10 km in size. This impact coincided with a time of heavy asteroid bombardment globally. Several other craters have been documented from a similar time, including one off the WA coast measuring 120 km in diameter. Another impact structure in Siberia was created by an asteroid 100 km in size."

The last sentence of that summary has _got_ to be a wording mistake. The impact CRATER in Siberia is 100km across. The impactor was (I just looked it up), "either an eight-kilometer diameter chrondrite asteroid, or a five-kilometer diameter stony asteroid." Indeed, an asteroid 100km across hitting the surface would leave something just a tad bit more noticeable than anything we've got so far, heh. And yes it would do really bad things to life on the planet; you're right on that count.

a 100km dense rock asteroid would sterilize the earth's surface. It would vaporize 343000 cubic miles of crust in less than a second.

Peak Overpressure: 6.89e+07 Pa = 689 bars = 9780 psi at 500km from impact. Actually at 500km from impact you'd be in the crater since it would be 520 miles in size. If it were possible to not be incinerated instantly, the pressure would probably cause you to explode as it dissipated. The wind would be 14900 mph

At 5000km from impact, you'd get hit with wind doing 978mph and get subjected to 54psi air pressure 4 hours after impact. This would kill you. Your body would be buried under 5.1 feet of ejecta

This is assuming a "Dense Rock" asteroid hitting the earth at a 45 degree angle, at 17000kph, which is the typical impact velocity. 11.8 RS earthquake would result over the entire earth. This is off the scale. It's nearly a quadrillion tons of seismic energy. It would split the earth. You would be launched high enough into the air to kill you from the impact when you came back down, if the acceleration didn't kill you. A nickel/iron one would be much worse.

The earth would most likely be an asteroid belt right now from this size of an impact at 45 degrees. It would survive an oblique impact, but the earth would get another moon and it would be an extinction event. The orbit would certainly be affected and the tides would change.

Yea it would be very messy and kill just about all multicellular animals. People would become extinct. There would be nowhere to hide on the earth's surface.

Correctly represented: the structure identified in the Timor Sea (the Mt. Ashmore dome [informaworld.com]) is 50km across, but it represents only the eroded central uplift of a complex crater [wikipedia.org], so the original crater diameter could have been 100km. The impactor for such a crater is roughly 10x as small (the 5 to 10km mentioned).

Incorrectly represented: the structure being referred to in Siberia is probably the Popigai crater [wikipedia.org], which is about 100km in diameter. This is incorrectly identified as the size of the impactor in both the summary and the article it cites.

Remaining puzzle: I don't know of any 120km-diameter impact crater "off the WA coast" of about the same age (i.e. ~Late Eocene). The Earth Impact Database [www.unb.ca] certainly doesn't show one, and the list of impact craters >100km is very short [www.unb.ca]. In fact, it is unlikely for such a crater to exist off the coast of Washington because the continent quickly changes to deep ocean crust due to the subduction zone parallel to the coast, I'm not sure the crust there is even Eocene in age (it's pretty young due to the adjacent Juan de Fuca ridge), and hardly any impact craters are known from ocean crust anyway (the only ones known are quite small, and didn't really form an "impact crater" because of the deep ocean water). It's possible that this "crater off Washington" was confused with the large (85km) Late Eocene impact structure that exists off the East Coast of the USA in Chesapeake Bay [wikipedia.org] and is not far from Washington, D.C..

Coincidentally both the Popigai impact and Chesapeake Bay impacts are mentioned in the abstract of the paper [informaworld.com], so it's very likely a mix-up about the two Washingtons that explains the third one. We can't really blame the submitter for the mix-up. They just quoted the errors in the other article.